Prolonged tack materials prepared from thermoplastic resins in a plasticizer are known which on heating become tacky or sticky and retain this tackiness for a considerable time even after cooling. This property, also known as delayed tack or setting, has been found useful in the preparation of adhesive compositions, as well as in thermography to produce a master which is imagewise exposed by means of heat, toned, and the toned image is then transferred onto an image receptor to provide a copy of the original image. In the above-described process, the prolonged tack property is present in the form of a continuous film over an imagewise tacky element. Conventional prolonged tack toners are used to develop the tacky image areas.
However, a subsequent transfer of the toned image using these toners onto an image receptor, does not result in a sufficient transfer of the toned image to an image receptor at low temperatures such as room temperature.
U.S. Pat. No. 4,461,823, issued to Held on July 24, 1984, describes multiple transfer of tacky image areas using prolonged tack toners wherein the toners can be prepared by combining a thermoplastic resin, e.g., polystyrene, with a plasticizer or a copolymer of methylmethacrylate (90)/methacrylic acid (10) and triphenyl phosphate plasticizer. A dye or colored pigment can be combined with the resin/plasticizer component. One of the main disadvantages with these toners is that it is difficult to transfer a sufficient amount of toner to an image receptor at a low temperature.
U.S. Pat. No. 4,469,625, issued to Held on Sept. 4, 1984, describes prolonged tack toners for the preparation of electric circuits. Examples of organic polymers and plasticizers are described in column 1 and include polystyrene and N-cyclohexyl-p-toluenesulfonamide, poly(methylmethacrylate)(90)/methacrylic acid(10) and triphenyl phosphate.